This invention relates to the art of enriching materials including isotopic elements, in selected isotopes of the elements.
In isotope separation an important parameter is the separation coefficient. Separation coefficient is a measure of the enrichment in a selected isotope achieved during a single separation operation or a plurality of cascaded operations. It can be defined by the equation: ##EQU1## where C.sup.I is the concentration of the selected isotope, of the isotopic element, whose enrichment is sought and C.sup.II is the concentration of the other isotopes of the element. The denominator (C.sup.I /C.sup.II).sub.INITIAL is the concentration ratio of the starting material, the numerator (C.sup.I /C.sup.II).sub.FINAL is the concentration ratio for the derived material. In this specification and in the claims the reference to "INITIAL" or "starting" or "first material" is intended to mean, not only a natural such material, but any material which has been previously enriched in an isotype and is processed for higher enrichment. The reference to "material" means a compound or compounds or minerals including the isotopic element as a component or the element alone. Where there are more than two isotopes, C.sup.II is the concentration of all the non-selected isotopes. Where, as in the case of uranium, there are only two isotopes, C.sup.II is the concentration of the non-selected isotope, for example U.sup.238 where U.sup.235 is the selected isotope.
Another factor governing isotope separation is the yield. The yield is the actual quantity or mass of enriched material which can be derived from an isotopic separation or from a cascaded series of such operations.
Isotope separation in accordance with the teachings of the prior art has failed to combine high separation coefficient and high yield except at excessively high cost. The electromagnetic method can be carried out at high separation coefficient but its yield is very small because the ion beam current which carries the isotopes must be small and must be passed through a narrow aperture. This method can yield only a fraction of a microgram in a single deposit operation for appreciable deposit requires many operations carried on for very long intervals. Methods capable of high yield, such as diffusion, rely on very small differences in the selective transport through the diffusion medium and have low separation coefficient. Selective vibrational excitation with tuned lasers in various ways has also been proposed. Typical of these methods is the two-step photo-dissociation. These methods are confronted with the requirement for isolation of the excited molecules from collisional excitation transfer and excitation exchange with non-selected isotopes and have failed to yield effective isotope enrichment.
It is an object of this invention to overcome the deficiencies of the prior art and to provide a method of enrichment which shall combine high separation coefficient with high yield.